Ejection device



Aug. 10, 1965 R. JUFFA EITAL 3,199,740

EJECTION DEVICE Filed Aug. 7, 1963 IN VENTORS I RICHARD JUFFA, HELMUTKRUGER, RUDOLF MICHAEL/5, HANS -JOACH/M REHBERG, JOSEF SU-/MAHL?HANS-HERMANN SCHULZ. t M

M ATTORNEYS United States Patent 3,19%,740 EJECTION DEVIQE Richard Juliaand Helmut Kriiger, Levcrkusen, and Eli!- dolf Michaelis,Cologne-Berlitz, and Hans-Joachim Rehherg, Josef Schmahl, andHans-Hermann Schulz, Leverkusen, Germany, assignars to FarhenfahrilrenBayer Alrtiengesellschaft, Leverkusen, Germany, a corporation of GermanyFiled Aug. 7, 1963, Ser. No. 309,428 Claims. (Cl. 222-146) The inventionrelates to an ejection device for ejecting and applying extremely smallquantities of compositions which are liquefied or softened by heataction, e.g. thermoplastic plastics, comprising an ejection cylinderwhich can be heated electrically and in which is displaceably arranged apiston fixed to the end of a push rod.

The heating of ejection cylinders has hitherto been effected byencircling them with electric heater strips or by induction. The expenseof equipment combined therewith is uneconomical for extremely smallejection devices. Furthermore, the use of such heating methods is notdesirable for such instruments for reasons of dimensions and weight. Thehigh heat capacity necessary with strip heating necessitates longheating up and cooling times and consequently the use of separatecooling means.

It has now been found that these disadvantages are obviated if theejection cylinder or a part thereof is heated according to the inventionby direct passage of electric current. Depending on the requirements ofthe local heating intensity and the heat conduction, the ejectioncylinder according to the invention has a wall thickness which increasesor decreases steadily or suddenly in the direction of ejection.

The result hereby obtained is that the heating and cool ing times of thecylinder are very short and thus the material being processed isprotected. When using the instrument as a dental ejector, theinconvenience to the patient is slight, due to the fact that it ispossible to dispense with an additional cooling. The direct heatting ofthe cylinder admits the use of the lowest possible voltages, e.g. 2volts, so that any danger to the patient or dentist is excluded.Moreover, the instrument can be made with extremely small dimensionssuch as have not so far been possible, e.g. with cylinder and nozzlediameter below mm. and even down to 1-2 mm, since heating coils,induction coils and cooling systems are omitted. The composition to besprayed is supplied as a granulated material or in the form of a smallrod to the cylinder.

The advancing movement of the piston can be effected manually or alsopneumatically.

For the pneumatic advancing movement and for the subsequent firmpressing of the ejected compositions on to the application surface, theejection cylinder is enclosed by a pneumatic pressure cylinder, which isprovided on the inlet side of the pressure medium with a closableopening or a resilient branch tube.

In the accompanying drawings:

FIGURE 1 is a diagrammatic longitudinal section through one embodimentof the complete device, and

FIGURE 2 is a diagrammatic longitudinal section showing the head of asecond embodiment of the device.

Referring to FIGURE 1, in a pressure cylinder ll, under the influence ofcompressed air supplied at 9, a piston 2 slides towards the left againstthe force of the spring 3 and carries with it a small ejection piston 5connected to the piston 2 by the piston rod 4. When the pressure isrelaxed, the spring 3, which is supported on an insulating guide member6 and the circlip 7, forces the piston back to its starting position,which is determined by engagement of the insulating cap 8 with thecylinder end. In the arrangement illustrated, an increase in pressure isproduced from the compressed air entering the nozzle 9 by blocking theend of a spring tube it), which forms the air outlet, by pressing thetube opening onto an elastic disc 11.

As shown in FIGURE 2, the blocking of the outlet can be etfected byclosing a suitably arranged opening 12 in a branch pipe 13 of thecompressed air supply by means of a finger.

The compressed air contributes to the cooling of the device when thepiston is not actuated. By using an inert gas instead of the compressedair, a protective gas atmosphere can be formed in addition to thedissipation of heat. For injecting into deep cavities and also forbetter cleaning, the small ejection piston can be advanced to beyond theopening of the ejection cylinder 13 surrounding it.

A sleeve 15 is inserted in the pressure cylinder 1 so that it can beeasily released by a bayonet connection 14, which sleeve co-axiallyretains the ejection cylinder 18 (made of corrosion-resistant metal ofhigh specific electrical resistivity) by means of a heat-insulatingintermediate member 16 and brazed webs 17 which are of low heatconductivity because of their small cross-section.

The ejection cylinder 13 is connected by conductors l9 and 2.8 to a lowvoltage source and is thus heated. By local reduction of the externaldiameter, the current density is increased at those places where higherheating capacity is required. The external diameter of the ejectioncylinder decreases for example towards the ejection aperture (FIGURE 1);on the other hand, for improving the heat conduction, the externaldiameter can be generally increased outside the electrically heatedregion (e.g. at the projecting tip). If desired, the orifice of theheated ejection cylinder can be constricted by screwing on a nozzle.

The sleeve 15', and also the pneumatic cylinder l, is coated with afluorolefine lining 21 or 22 which is made suitable for gripping (e.g.by sand-blasting), the tube It? being embedded in said lining. Thelining 21 has an opening which is connected through bores to theatmosphere and is also cooled by the air stream discharging from thetube lit in the rest position. One or both electrical conductors can beplaced inside the compressed air tube adjoining the nozzle 9 forpurposes of better handling.

The device operates as follows:

A small rod of suitable dimensions of thermoplastic material or a fewgranules thereof are placed in the opening of the cylinder 18. Theopening-is then optionally constricted by screwing on a nozzle. Theheating is switched on and off or increased and reduced by atemperaturecontrolled switch or a time switch adjusted to valuesobtained by experience. The device is gripped like a pencil and ispositioned on the cavity which is to be filled, which is possiblypreheated or is pretreated with a solvent or even with a release agent.Finger pressure on the small tube to discharging cooling air in the restposition figure or closing of the opening 12 (FIGURE 2) leads to the hotcomposition being ejected by means of the mechanism described; pressurecan be maintained as long as desired by means of the piston, whereby aunion with the foundation material and good filling of the cavity isguaranteed and any possible occurring shrinkage compensated for.

We claim:

it. An ejection device for extruding thermoplastic ma terial, whichcomprises:

(a) A support housing;

(b) A tubular ejection cylinder for receiving material to be extrudedtherefrom, said cylinder being made of an electrically conductivematerial having a selected resistivity for heating said material inresponse to an electrical current passed through said cylinder, therebyconverting said material from a solid to a plastic state;

(c) Means connected to said housing for supporting said ejectioncylinder;

(d) A piston slidably disposed within said ejection cylinder forextruding said material therefrom;

(e) Electrically conductive means for passing an electrical currentthrough said ejection cylinder; and,

(f) Pneumatic actuating means for driving said piston whereby saidmaterial is extruded from the ejection cylinder in a plastic state.

2. The ejection device of claim It wherein the eiectri current forheating the iaterial flows in an axial direction through the wall ofsaid ejection cylinder, said wall having a thickness which variesaxially so as to provide a predetermined axial distribution ofresistance throughout said cylinder for controlling the heating of thematerial therein.

3. The ejection device of claim 1 wherein the pneumatic actuating meansfor driving the piston includes a pneumatic actuating cylinder having apiston connected to the piston within the ejection cylinder and anexternal-- ly disposed air bleed orifice in the air supply line to saidpneumatic cylinder whereby the ejection of material can be controllablyvaried by blocking said orifice.

4. The ejection device of claim 1 wherein the pneumatic actuating meansfor driving the piston includes a pneumatic actuating cylinder having apiston connected to the piston within the ejection cylinder, an airsupply line connected to said actutaing cylinder, and a spring tube airdischarge line, also connected to said actuating cylinder, said springtube having an open end for the dis charge of air therefrom, saiddischarge end being disposed adjacent to a resilient closure discailixcd to the housing, whereby the ejection of material can becontrollably varied by pressing said spring tube discharge end intoabutting contact with said closure disc.

5. The ejection device of claim 1 wherein the ejection cylinder isdisposed within an electrically conductive sleeve which is secured tothe support housing, said cylinder being supported in spaced relation tosaid sleeve by means of an electrically conductive spacer and anelectrically insulating spacer whereby said sleeve and conductive spacerform part of an electrically conductive path for passing an electriccurrent through said ejection cylinder.

References Cited by the Examiner UNITED STATES PATENTS 1,575,152 3/26 DiBattista 222146 2,086,462 7/37 Bost 222146 X 2,272,780 2/42 Schweyer2Z2-l46 X 2,567,960 9/51 Myers 222146 X EVERETT W. KIRBY, PrimaryExaminer.

HADD S. LANE, Examiner.

1. AN EJECTION DEVICE FOR EXTRUDING THERMOPLASTIC MATERIAL, WHICHCOMPRISES: (A) A SUPPORT HOUSING; (B) A TUBULAR EJECTION CYLINDER FORRECEIVING MATERIAL TO BE EXTRUDED THEREFROM, SAID CYLINDER BEING MADE OFAN ELECTRICALLY CONDUCTIVE MATERIAL HAVING A SELECTED RESISTIVITY FORHEATING SAID MATERIAL IN RESPONSE TO AN ELECTRICAL CURRENT PASSEDTHROUGH SAID CYLINDER, THEREBY CONVERTING SAID MATERIAL FROM A SOLID TOA PLASTIC STATE; (C) MEANS CONNECTED TO SAID HOUSING FOR SUPPORTING SAIDEJECTION CYLINDER;